First radioactive sludge retrieved at Sellafield

The first radioactive sludge has been removed from the Sellafield nuclear site years after devising an engineering solution to suck up the goo from the bottom of the pond where it is stored.

Thought to be one of the most hazardous nuclear plants in Europe, the First Generation Magnox Storage Pond (FGMSP) needs to be emptied of 1500 cubic metres of radioactive sludge – the equivalent of more than half an Olympic sized swimming pool.

The FGMSP was built to store, cool and prepare used Magnox nuclear fuel for recycling into new fuel, and during its 26-year operating lifeline it processed about 27,000 tonnes of fuel.

Martin Leafe, head of the FGMSP, said in a statement: “We’re making history at Sellafield by transferring the first sludge using a tried and tested pump to a new £240m state-of-the-art sludge storage plant containing three enormous stainless steel buffer storage vessels, each of which is the same volume as seven double-decker buses.”

The site clearance began in November 2005 and revolves around a small-scale specialist centrifugal pump that was sent to the depths of the pond to lift the first sludge. The pump is fitted to the underside of a large pontoon which has four thrusters to propel it around the pond.

The pump itself is equipped with a 60cm-long ‘hoover hose’ and can be raised or lowered by remote control to suck up the sludge and mix it with water to turn it into a slurry, which can be pumped across to the new sludge plant.

“We transfer the sludge in batches to the new plant where it settles in one of the enormous buffer storage tanks and then the top layer of water is sent back to the pond," Leafe explained.

During the process water must be left in place as the sludge is removed to provide a radioactive shield for the stored nuclear fuel and reduce the “inherent hazard posed by the facility”.

“It will take several months of work to transfer enough sludge to fully test and commission the sludge plant and in parallel we’ll install the bulk sludge removal equipment,” Leafe said.

However, the job is not seamless as the platform needs to be driven remotely from a control cabin to minimise the radiation dose to the workforce.

“The pond is very congested and full of large metal boxes containing nuclear fuel, so we need to work around these and ensure these remain fully submerged at all times,” Leafe added.

Just like in any other garden pond, sludge has also been accumulating at the bottom of the pond as it was built with no roof and as a result it is made up of nuclear fuel corrosion products, algae and windblown material.

Andy Lindley, the Office for Nuclear Regulation (ONR) lead of the Sellafield Programme, said: “This is a complex operation and a first of its kind at Sellafield. There will be challenges in removing this material and we acknowledge that there may be some setbacks.”

The surge in technological solutions to help clear nuclear sites has led to deploying an advanced robotic arm at Japan’s Fukushima power plant, as E&T newsreported, to fix leaks of contaminated water, as well as a snake-like inspection robot in preparation for examining one of the three melted reactors.